The present invention relates to the therapeutic use and the biological activity of triterpenoid derivatives. The invention further relates to novel triterpenoid derivatives.
To date, the prior art has primarily focussed on compounds that are capable of regulating the cell cycle by virtue of inhibiting cyclin dependent kinases (CDKs). Examples of such compounds include butyrolactone I, flavopiridol, 10 bohemin, olomoucine, roscovitine, purvanalol and indarubicine.
There is considerable support in the literature for the hypothesis that CDKs and their regulatory proteins play a significant role in the development of human tumours. Thus, in many tumours a temporal abnormal expression or activity of CDKs has been observed, together with a major deregulation of protein inhibitors (mutations, deletions). This results in the activation of CDKs and consequently in defective regulation of the G1/S transition. Unlike normal cells, tumour cells do not arrest in G1, and since they become independent of growth factors, they pass the G1 restriction point and enter the S phase very rapidly.
In contrast to the prior art, the present invention relates to compounds which are anti-proliferative, but which are believed to operate via a mechanism other than CDK inhibition.
The Gi/S transition of the mammalian cell cycle is tightly regulated by the retinoblastoma protein (pRb). Retinoblastoma gene mutations or deletions predispose individuals to familiar retinoblastoma and other types of cancers. The pRb protein is a docking protein, which in hypophosphorylated form has the capacity to bind and thus to inactivate S-phase transcription factors such as DP-1 and E2F. However, following phosphorylation by G1/S cyclin-dependent kinases (CDKs) (CDK4/cyclin D1-D3, CDK6/cyclin D1-D3, CDK2/cyclin A), hyperphosphorylated pRb releases the transcription factors and S phase is initiated. Within the S phase, the pRb protein phosphorylation is maintained by the activity of CDK2/cyclin E complexes. Thus, hyperphosphorylation of the pRb protein plays a key role in the molecular pathology of cancer cells with altered CDK activity.
The present invention relates to the use of triterpenoid compounds derived from the natural products betulin and betulinic acid (BA) as shown in formula (A). The compounds of the present invention are referred to hereinafter as betulinines.

With regard to their biological and therapeutic activity, the compounds disclosed herein are believed to be of specific benefit in the treatment of proliferative diseases such as cancers and leukaemias.
Several of the compounds suitable for use in the present invention are already known in the art, for example those disclosed in Ber. Dtsch. Chem. Ges. 55, 2332 (1922), Schluze, H. et al; Acta Chem. Scand., B 29, 139 (1975), Suokas E. et al; Collect. Czech. Chem. Commun. 56, 2936 (1991), Sejbal J. et al; Collect. Czech. Chem. Commun. 64, 329 (1999), Klinotová et al; Indian. J. Chem., Sect. B 34, 624 (1995), Dinda B. et al; Chem. Listy 91, 1005 (1997), {hacek over (S)}arek J. et al. However, these disclosures do not include any indication as to possible biological activity of such compounds.
A first aspect of the present invention relates to the use of a compound of formula I, or a pharmaceutically acceptable salt thereof, in therapy,
wherein:                X1 is C═O, C═NOR1a, CHOR1a, CHOCOR1a, CHOCOY-Hal, CHOC(O)OR9, CHOC(O)OR1a, CHOC(O)OR10, and Hal is Br, Cl, I, F;        X3 is C═O, CHOR1b, CHOCOR1b, or X3 and R8 together are CHOCOCH2 and form a spirolactone;        R1-5 are each independently H or lower alkyl;        R6 is H or absent if “a” is a double bond;        R7 is H, COOR1c, YOCOR1c, COOYOCOR1e, YCOOR1e;        R8 is H, COOR1d, YCOOR1d, YCOOR10, YCOHal, COOYOCOR1d, CH2OR1d, CH2COCOR1d, COCOCOR1d         or R7 and R8 together are ═CH2 or CH2OCOCH2;        R9 is an OH-substituted alkyl group, an ether group or a cyclic ether;        R10 is lower alkyl substituted by Hal        “a” is a double bond or a single bond        and wherein Y═(CH2)n                     n=0 to 5;            R1a-1d are the same or different groups of R1.                        
In a preferred aspect, the invention relates to the use of a compound of formula I, or a pharmaceutically acceptable salt thereof for treating a patient suffering from leukaemia, cancer or other proliferative disorder.
A second aspect of the present invention relates to novel betulinines of structural formula Ia, or pharmaceutically acceptable salts, thereof;
wherein:                X1 is C═O, C═NOR1a, CHOR1a, CHOCOR1a, CHOCOY-Hal, CHOC(O)OR9, CHOC(O)OR1a, CHOC(O)OR10, and Hal is Br, Cl, I, F;        X3 is C═O, CHOR1b, CHOCOR1b, or X3 and X8 together are CHOCOCH2 and form a spirolactone;        R1-5 are each independently H or lower alkyl;        R6 is H or absent if “a” is a double bond;        R7 is H, COOR1c, YOCOR1c, COOYOCOR1e, YCOOR1e;        R8 is H, COOR1d, YCOOR1d, YCOOR10, YCOHal, COOYOCOR1d, CH2OR1d, CH2COCOR1d, COCOCOR1d         or R7 and R8 together are ═CH2 or CH2OCOCH2;        R9 is an OH-substituted allyl group, an ether group or a cyclic ether,        R10 is lower alkyl substituted by Hal        “a” is a double bond or a single bond        and wherein Y═(CH2)n                    n=0 to 5;            R1a-1d are the same or different groups of R1 with the proviso that                            (i) when X1 is CHOAc, X3 is C═O, “a” is single bond, R1-5 are Me, R6 is H;            when R7 is CH2OAc, R8 is other than COOH, CH2COCOPri, COCOCOPri, CH2COOH, or CH2CH2COiPr;        when R7 is CO2Me, R8 is other than CH2CH2COCH(CH3)2;        when R7 is H, R8 is other than H, CH2COOMe, CH2COOH or CH2CH2COPri; and            (ii) when X1 is CHOH, X3 is C═O, “a” is single bond, R1-5 are Me, and R6 is H,            when R7 is H, R8 is other than H, CH2COOH, CH2CH2COCH(CH3)2 or CH2COOMe;        when R7 is CH2OAc, R8 is other than CH2COOH;        or a pharmaceutically acceptable salt thereof.        
As used herein, the term lower alkyl means a linear or branched chain alkyl group containing from 1 to 6 carbon atoms, including methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tertiary butyl.